Generally, filter pads are universal enough that they fit standard containers. Commonly, dewatering containers are based on a roll-away dumpster design, also known in the industry as roll-off containers. There are basically two varieties of these dewatering containers: those that have permanent filters and those that use disposable filters.
Container filters can be trailer-mounted for easy hauling, or permanently mounted on a tipping stand so that the cake can be unloaded on site. Within the permanent filter category there are multiple configurations of filter orientation, materials of construction, and filter porosity. The most common type of disposable filter is a needle punched polypropylene geotextile. This material is typically folded in half lengthwise and the ends sewn together creating an “envelope”. It is then inserted into a container with the top edges folded over the top sides of the container.
The support structure for the disposable filters can be bar grating, expanded metal, perforated plate or other rigid porous material that can support the weight of the solids. These plates are set off from the sides and bottom so that liquids can drain from the material and then be decanted. There are usually drain ports in the container through which the effluent is discharged. These are typically placed on the bottom of the container or at the bottom of the door and have a shut off valve and safety cap. In rare cases, of a roll-off type disposable filter box, the door can simply be left slightly open (but secured with a latch).
Most often, dewatering boxes are used on a variety of waste streams and are allowed to gravity drain in whatever time frame was necessary to reach the desired cake dryness. Effluent water from a dewatering box can go back to the headworks of the plant virtually devoid of solids or removed by a vacuum truck or similar means.
The main reason to choose a dewatering container is their simple operation. The dewatering container itself has no moving parts. The waste is processed in the same unit in which it is hauled away and dumped, thus limiting the handling of the sludge. The dewatering box will give volume reductions in the 80% to 95% liquid range depending on the percent solids in the sludge. The cake produced by the dewatering box will pass the “paint filter” test and can go to the local landfill. The effluent water from the dewatering box can go back to the headworks of the plant virtually devoid of solids.
To empty the container, the operator generally cuts the filter with a knife and dumps the content. The process is inefficient and sometimes dangerous. There is no way to control the solids dumping from the container as the operator cuts the pad. This positions the operator in close proximity to the material and, in most cases, the operator contacts the solids as they dump.
Likewise, once the dewatered contents contained in the filter are emptied, the process of removing the filter from the container itself must be accomplished. This routinely requires the operator to enter the container and “cut” or “tug” the liner free of the container. In some cases, mechanical equipment. such as a backhoe, must be used to expedite the process. This procedure places the operator in a dangerous environment.
Accordingly, it remains desirable in the pertinent art to provide filter pad to address the limitations associated with known filter pads, including but not limited to those limitations discussed above.